Light-emitting element, light-emitting device using the light-emitting element, and transparent substrate used in light-emitting elements

ABSTRACT

In order to improve the light extraction efficiency of a light-emitting element, the light-emitting element includes: a light-emitting layer provided between an electrode and a transparent substrate; a particle layer provided between the light-emitting layer and the transparent substrate; and an adhesive layer provided between the light-emitting layer and the particle layer, the particle layer includes particles having a refraction index that is higher than a refraction index of the transparent substrate, the adhesive layer has a refraction index that is higher than the refraction index of the transparent substrate, and the particle layer has an average thickness that is less than an average particle size of the particles.

TECHNICAL FIELD

The present invention relates to a light-emitting element, alight-emitting device using the light-emitting element, and atransparent substrate used in the light-emitting element.

BACKGROUND ART

Many manufacturers are competing to develop an electroluminescenceelement (OLED element) made of an organic material for an applicationsuch as a thin and space-saving illumination or a display.

The greatest challenge is to improve the external light extractionefficiency of the element. This is because more than half of the lightemitted from inside the element cannot be output to the outside of theelement due to the effect that the emitted light is reflected by atransparent electrode or the like having a high refraction index in themiddle of exiting the element or other such effects. To address thisproblem, there have been proposed several approaches of providingvarious layers (light extraction efficiency improving layers) forimproving the light extraction efficiency to the transparent electrodeor the like.

Patent Literatures 1 and 2 propose improving the light extractionefficiency by providing on the transparent electrode a layer in whichparticles are dispersed in a binder, the particles having a refractionindex that is different from that of the binder. Further, Non PatentLiterature 1 proposes improving the light extraction efficiency byproviding a layer formed of a titanium oxide thin film having voidstherein.

In Patent Literatures 1 and 2, the binder layer containing the particlesinvolves an organic solvent and is thus formed by, instead of a vacuumprocess, preparing a mixture of the binder, the powders, and the organicsolvent, and applying and drying the mixture under normal pressure. InNon Patent Literature 1, the layer is also formed on the transparentelectrode under normal pressure by spin coating. In Patent Literatures 1and 2, and Non Patent Literature described above, the light extractionefficiency improving layer is provided on the transparent electrode.

Prior Art Document Patent Document

-   [Patent Document 1] JP 2004-296437 A-   [Patent Document 2] JP 2007-273397 A

Non-Patent Document

-   [Non-Patent Document 1] The 55th Meeting of The Japan Society of    Applied Physics and Related Societies 30 a-ZA-1 (2008.3.30)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Incidentally, there is a light-emitting layer made of an organicmaterial inside a transparent electrode of an OLED element, whichdegrades in light-emitting property when touched by an organic solventdue to swelling, dissolution, or the like. Further, the light-emittinglayer made of the organic material undergoes heat denaturation whenheated, with the result that the light-emitting property is reduced toemit no light in some cases.

In addition, the transparent electrode is formed by spattering or thelike, which may form nanoscale gaps at the surface of the layer.Therefore, when liquid containing an organic solvent is applied on thetransparent electrode, the organic solvent may infiltrate from thenanoscale gaps to contact the light-emitting layer. Further, drying thesolvent and curing the binder involve a heating process, which may causea thermal damage to the light-emitting layer. Accordingly, when thelight extraction efficiency improving layer containing particles isprovided on the transparent electrode, the light-emitting layer may bedamaged to reduce the light extraction and utilization efficiency.

It is an object of the present invention to improve the light extractionand utilization efficiency of the light-emitting layer.

Means for Solving the Problems

In order to solve the above-mentioned problem, alight-emitting elementaccording to the present invention includes: a light-emitting layerprovided between an electrode and a transparent substrate; a particlelayer provided between the light-emitting layer and the transparentsubstrate; and an adhesive layer provided between the light-emittinglayer and the particle layer, in which the particle layer has arefraction index that is higher than a refraction index of thetransparent substrate.

Effect of the Invention

According to the present invention, the light extraction efficiency ofthe light-emitting element may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A sectional structure of a light-emitting element according to thepresent invention.

FIG. 2 A production process of the light-emitting element according tothe present invention.

FIG. 3 An example of a particle surface modification process of aparticle layer used in the light-emitting element according to thepresent invention.

FIG. 4 A sectional structure of an adhesive layer of the light-emittingelement according to the present invention.

FIG. 5 Examples of structure of grooves of the adhesive layer of thelight-emitting element according to the present invention.

FIG. 6 A production process of the light-emitting element according tothe present invention.

FIG. 7 Another production process of the light-emitting elementaccording to the present invention.

FIG. 8 A schematic sectional view of the light-emitting elementaccording to the present invention.

FIG. 9 A schematic sectional view of the light-emitting elementaccording to the present invention.

FIG. 10 A schematic sectional view of the light-emitting elementaccording to the present invention.

FIG. 11 A schematic sectional view of the light-emitting elementaccording to the present invention.

FIG. 12 The light-emitting element according to the present invention.

FIG. 13 The light-emitting element according to the present invention.

FIG. 14 A casing of a light-emitting device according to the presentinvention, in which a plurality of light-emitting elements areconnected.

FIG. 15 The light-emitting device according to the present invention.

FIG. 16 The light-emitting device according to the present invention.

FIG. 17 The light-emitting device according to the present invention.

FIG. 18 The light-emitting device according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the accompanying drawings, embodiments of the presentinvention are described.

FIG. 1 is a schematic sectional view illustrating a light-emittingelement according to the present invention. A light-emitting layer isprovided between a transparent electrode and an electrode. An adhesivelayer, a particle layer, and a transparent substrate are provided on theside of the transparent electrode opposite to the side on which theelectrode is provided. Aluminum or other such materials having highreflectivity are used for the electrode, and hence most of light emittedfrom the light-emitting layer travels to the transparent electrode side.With the above-mentioned configuration, light leaks from a contactportion between particles having a high refraction index and an adhesivelayer and is scattered by the particles, with the result that the effectof extracting light is presumably improved.

FIG. 2 illustrates a process of forming the light-emitting element ofFIG. 1. The particle layer is formed on the transparent substrate. Theresultant is referred to as an intermediate part 1. A structure isformed of the transparent electrode, the light-emitting layer, and theelectrode, and the adhesive layer is formed on the transparent electrodeside. The resultant is referred to as an intermediate part 2. Theparticle layer side of the intermediate part 1 is bonded to the adhesivelayer of the intermediate part 2 to form the light-emitting element. Theadhesive layer may be attached to the particle layer side of theintermediate part 1 instead of the intermediate part 2. Glass is morepreferred as the material of the transparent substrate than a resin interms of the solvent resistance and the hardness. In the case of theresin, there is a disadvantage that an acrylic board having a relativelyhigh hardness exhibits high moisture absorption. To address thisproblem, the acrylic board is coated with a resin having low moistureabsorption, for example, a cycloolefin-based resin to suppress moistureabsorption, to thereby enable the use for the transparent substrate.

A method of forming the particle layer in a case where a binder is usedis described. First, in order to increase the dispersibility in thesolvent and to suppress agglomeration of the particles after theapplication, surfaces of the particles are chemically modified with asilane coupling agent. The particles of the particle layer are dispersedin an organic solvent together with a small amount of a binder material.In this manner, a coating for forming the particle layer is prepared.The coating is applied on the transparent substrate and the bindermaterial is cured to form the particle layer.

In order to bind the silane coupling agent to the surfaces of theparticles of the particle layer, the silane coupling agent is firstadded to the organic solvent, to which the particles of the particlelayer are added and stirred for several hours. After the solvent isvolatilized by an evaporator, the particles of the particle layer areheated at 120° C. for 30 minutes. In this manner, the silane couplingagent is bound to the surfaces of the particles of the particle layer bysilicon-oxygen coupling. When the additive amount of the silane couplingagent used is too large, there is a higher chance for the particles ofthe particle layer to agglomerate after being applied to the substrate.Therefore, the surface area of the particles of the particle layer ismeasured in advance by the BET theory or the like and the requisiteminimum amount of the silane coupling agent for coating the area isused, to thereby prevent the agglomeration of the particles.

It is preferred that the binder material be a material that forms abinder of an inorganic oxide such as silica sol or titania sol, whichhas high affinity with the inorganic particles. Further, in a case wherean organic resin is used, it is preferred to use an epoxy resin whichhas high adherence with the inorganic particles. Other preferred organicmaterials are an acrylic resin, a polycarbonate resin, and the like,which are highly transparent.

The silane coupling agent as used herein refers to a silane couplingagent in which two or three alkoxysilane groups are bonded to a siliconatom, or a silane coupling agent in which two or three chloro groups arebonded to a silicon atom. As the substituent for silicon other than analkoxysilane group and a chloro group, Structure group 1 and Structuregroup 2 described below are suitable for the dispersion of particles inthe particle layer.

(Structure Group 1)

—(CH₂)₃NHCOCH₃, —(CH₂)₃NHCOCH₂CH₃, —(CH₂)₃NHCOC₃H₇, —(CH₂)₃NHCOC₄H₉,—(CH₂)₃NHCOC₅H₁₁, —(CH₂)₃NHCOC₆H₁₃, —(CH₂)₃NHCOC₇H₁₅, —(CH₂)₃NHCOC₈H₁₇

Structure group 1 is produced by: preliminarily allowing a silanecoupling agent having a —(CH₂)₃NH₂ group to bind to the surfaces of theparticles of the particle layer; and then allowing the correspondingcarboxylic acid to react with the amino group.

(Structure Group 2)

—(CH₂)₃NHCO₂CH₃, —(CH₂)₃NHCO₂CH₂CH₃, —(CH₂)₃NHCO₂C₃H₇, —(CH₂)₃NHCO₂C₇H₉,—(CH₂)₃NHCO₂C₅H₁₁, —(CH₂)₃NHCO₂C₆H₁₃, —(CH₂)₃NHCO₂C₇H₁₅,—(CH₂)₃NHCO₂C₈H₁₇

Structure group 2 is produced by: preliminarily allowing a silanecoupling agent having a —(CH₂)₃NCO group to bind to the surfaces of theparticles of the particle layer; and then allowing the correspondingalcohol to react with the isocyanate group.

In addition to the silane coupling agents described above, a silanecoupling agent having an isocyanate group, a vinyl group, a3-glycidoxypropyl group, or a 3-chloropropyl group is suitable for thedispersion of particles in the particle layer.

Hydrocarbon substituents such as —C₆H₁₃, —C₈H₁₇, and —C₁₀H₂₁, oraromatic substituents, such as —C₆H₅ and —C₁₀H₇ may improvedispersibility in the solvent, but have low dispersibility when formedinto a film, with the result that the agglomeration of the particles isprone to occur. Using a silane coupling agent having a binding sitehaving a heteroatom, such as amide linkage, in a substituent tends toprovide good dispersibility when formed into a film.

A method of forming the particle layer in a case where the binder is notused is described. The particles of the particle layer having chemicallymodified surfaces are produced by chemically binding a transparentsubstrate having a chemically modified surface. FIG. 3 schematicallyillustrates the method.

The transparent substrate is treated with a silane coupling agent (A).This silane coupling agent has a substituent A. Further, the particlesof the particle layer are treated with a silane coupling agent (B). Thissilane coupling agent has a substituent B. The substituents A and B areselected so as to form a chemical bond with each other. Next, theparticles of the particle layer and the transparent substrate, whichhave been treated with the silane coupling agents, are reacted to form achemical bond between the transparent substrate and the particles of theparticle layer. Finally, washing is performed to remove particles of theparticle layer that are not bonded to the transparent substrate. In thismanner, the particle layer is formed on the transparent substrate. Whenan amino group is selected as the substituent A, a silane coupling agenthaving, for example, a glycidyl group as the substituent B is selected.The substituents may be exchanged so that the substituent A is aglycidyl group and the substituent B is an amino group. Further, achlorine group may be selected instead of the glycidyl group.Substituents having a double bond, such as a vinyl group, may beselected for both the substituents A and B. The double bonds may bereacted to form a single bond and to bond the particles of the particlelayer and the transparent substrate at the same time.

The particles constituting the particle layer need to have a refractionindex that is higher than that of the transparent electrode. Thetransparent electrode, which is made of ITO or IZO, has the refractionindex of approximately 2.1. It has been found from our study that therefraction index of the particles needs to be equal to or higher thanthe refraction index of the transparent electrode in order to causeleakage of light. Therefore, particles having a refraction index of 2.1or higher are selected. Further, in a case of illumination, it isdesired that the particles be white or a pale color in the visible rangeso as not to color the emitted light. Specifically, there are giventitanium oxide (refraction index: 2.5 to 2.7), zirconium oxide(refraction index: 2.4), barium titanate (refraction index: 2.4),strontium titanate (refraction index: 2.37), bismuth oxide (refractionindex: 2.45), and the like. This ensures that the tone of the lightemitted from the light-emitting element in the case where the particlelayer is formed to be substantially the same as the case where theparticle layer is absent. Further, when a desired color of the emittedlight is chromatic, particles having a color similar to the desiredcolor may be used. For example, blue particles such as copper oxide(refraction index: 2.71) may be used when blue light is to be emitted,red particles such as ferric oxide (refraction index: 3.01) may be usedwhen red light is to be emitted, and yellow particles such as cadmiumoxide (refraction index: 2.49) may be used when yellow light is to beemitted.

The particles forming the particle layer act as a diffraction gratingwhen arranged regularly, and the wavelength of the extracted light isdetermined by the particle size, with the result that the otherwavelengths cannot be extracted. Therefore, the particles are arrangedirregularly so that light in a wider wavelength range may be extracted.Further, when the particles overlap each other due to the agglomerationor the like, the extracted light is apt to scatter, with the result thatthe brightness at the front is reduced. Therefore, it is desired thatone particle be formed at any given point on the transparent substrateso that the particles forming the particle layer do not overlap eachother.

When the particles in the particle layer are in contact with each other,the extracted light reenters the adjacent particle in contact from thecontact portion to lower the extraction efficiency. Therefore, it isdesired that the particles be not in contact with each other. When theparticles are prevented from being in contact with each other, theaverage thickness of the particle layer becomes less than the averageparticle size of the particles. In other words, in order to improve thelight extraction efficiency, it is desired that the average thickness ofthe particle layer be set less than the average particle size of theparticles.

It is preferred that the particles forming the particle layer be aninorganic oxide, which is resistant to denaturation. It is furtherpreferred when the binder material is silica sol, which has high bindingproperty with respect to an oxide.

As a result of study on the particle size, it has been found that thepreferred average particle size is 80 to 200 nm when light in thevisible range (of measured wavelengths of 360 to 760 nm) is to beextracted. In particular, the average particle size of 90 to 190 nmresulted in high extraction efficiency. In the case of particle size ofsmaller than 80 nm or larger than 200 nm, the light extractionefficiency for visible light was reduced. The reason is that theparticle size probably relates to the wavelength of the extracted lightbecause, as the particle size becomes smaller, the extraction efficiencyfor short wavelengths becomes higher and the extraction efficiency forlong wavelengths becomes a little lower. The particles have a highspecific density. For example, zirconium oxide has a specific density of6.1, titanium oxide has a specific density of 4.1 to 4.2, and bariumtitanate has a specific density of 6.1. Therefore, the surfaces of theparticles are chemically modified with the silane coupling agent toincrease dispersibility in the solvent.

The adhesive layer, which is a resin layer having a low elasticity, mayin some cases contain fine particles having a high refraction index inthe resin and is provided between the transparent electrode and theparticle layer. When the transparent substrate is flat, the particles ofthe particle layer and the adhesive layer should be brought into contactwith each other without applying a pressure on the transparentsubstrate. However, in reality, the transparent substrate has undulationor the like and is not always flat. Therefore, if the adhesive layerdoes not deform at all, there arises a probability that some of theparticles of the particle layer are not brought into contact with theadhesive layer. To address this problem, the storage elastic modulus ofthe adhesive layer is reduced so that, when a pressure is applied viathe transparent substrate, the adhesive layer may be deformed to bebrought into contact with the particles of the particle layer.Specifically, it is preferred that the storage elastic modulus be 100kPa or less. This is because the storage elastic modulus of 100 kPa orless allows the particles of the particle layer and the transparentelectrode to be brought into close contact with each other even if theglass has undulation of several μm. It should be noted, however, thatthe storage elastic modulus needs to be 1 kPa or more because, when thestorage elastic modulus is too low, there is a fear that the transparentsubstrate may slide off the transparent electrode. Further, the lowerlimit of the indoor operating temperature under which the light emittingelement is generally used is about 10° C. Therefore, setting the storageelastic modulus of the adhesive layer to 1 kPa to 100 kPa at 10° C.allows the particles of the particle layer and the transparent electrodeto be brought into close contact with each other.

The extraction efficiency tends to be high when the adhesive layer has ahigh refraction index. Therefore, it is more preferred when particles oftitanium oxide, zirconium oxide, barium titanate, or the like are addedin a transparent resin. The refraction index is increased by 0.3 to 0.4when the particles are contained in 10 to 30 wt % (refraction index:about 1.65 to 1.8) as compared to when no particle is contained(refraction index: about 1.45 to 1.55). Further, it is preferred thatthe size of the fine particles to be added be 5 to 50 nm in averageparticle size. When the size is larger than 50 nm, the adhesive layerbecomes cloudy. When the size is smaller than 5 nm, on the other hand,the bulk density is reduced, with the result that the particles easilyscatter and become hard to handle. It is preferred that the particles bean inorganic oxide. This is because inorganic oxides are chemicallystable and do not change in tone even after being irradiated with theemitted light for a long period of time.

The method of producing the adhesive layer is to form a film of anadhesive resin for attachment, or to apply a monomer for forming theresin and then cure the monomer. The monomer of the adhesive layer maybe made of the following materials. The adhesive layer is formed byadding a curing agent for facilitating the curing by light, heat, or thelike to the materials, and then curing the materials.

Examples of the acrylic materials include methyl methacrylate, ethylmethacrylate, propyl methacrylate, isopropyl methacrylate, butylmethacrylate, isobutyl methacrylate, hexyl methacrylate,octylmethacrylate, 2-ethylhexylmethacrylate, decyl methacrylate, dodecylmethacrylate, methyl acrylate, ethyl acrylate, propyl acrylate,isopropyl acrylate, butyl acrylate, isobutyl acrylate, hexyl acrylate,octyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, dodecyl acrylate,and the like. Other examples thereof include: ethylene glycol, propyleneglycol, diethylene glycol, 1,3-dihydroxycyclobutane,1,4-dihydroxycyclohexane, 1,5-dihydroxycyclooctane, and the like, eachof which has a plurality of hydroxy groups in a molecule; ethyleneglycol monoglycidyl ether, ethylene glycol diglycidyl ether, each ofwhich has a glycidyl group in a terminal; a monomer having a cyclicportion such as a cycloalkane ring, an aromatic ring, or a norbornenering at a side chain; a monomer having a bisphenol A-like skeleton; andthe like.

Of the materials, an acrylic resin is used alone or in combination witha plurality of other types of resin to form the adhesive layer. Theadhesive layer may be formed also by copolymerizing the materials withanother polymer. The polymer to be used may include polyacrylic acid,polyvinyl alcohol, polyallyl amine, or the like. Alternatively, apolymer such as an acrylic resin, a urethane resin, or the like, whichis already polymerized and has no reactive site for a monomer, may bedissolved in the monomer to be used, to thereby reduce shrinkage duringthe curing.

In order to reduce the storage elastic modulus, the material to be usedis specifically a material having a glass transition temperature (Tg)that is equal to or lower than the room temperature. This is because aresin at a temperature that is equal to or lower than Tg is reduced inelasticity. An acrylic monomer has lower Tg as the number of carbonatoms in the side alkyl chain becomes larger. In order to set Tg to atemperature that is equal to or lower than the room temperature, it isparticularly desired that the number of carbon atoms in the side chainof the acrylic monomer be about 4 or more so that enough flexibility andlow elasticity may be given to the resin.

If the same monomer is used, it is more preferred when the resin has alower average molecular weight because the elasticity is reduced. Inorder to reduce the average molecular weight, it is possible to increasethe additive rate of a catalyst to be used in the curing. Further, in acase where light cure is used as the method of curing the monomer, theintensity of the irradiated light may be reduced to reduce the averagemolecular weight of the resin to be formed. In a case where heat cure isused, the average molecular weight of the resin to be formed may bereduced by using an initiating reagent that allows curing at as low atemperature as possible and performing the curing at as low atemperature as possible.

Another method may be to add a plasticizer. It is desired that theplasticizer to be added be dispersed uniformly in a frame so that theelasticity of the frame does not become non-uniform among differentplaces. Therefore, it is preferred that the plasticizer be dissolved ina monomer. For example, in the case of using an acrylic monomer, adesired plasticizer is a phthalic acid ester having an ester bond in itsstructure, or an ester-based compound such as an adipic acid ester.

Specific examples of the phthalic acid ester include dimethyl phthalate,diethyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate,di-n-octyl phthalate, diisononyl phthalate, dinonyl phthalate,diisodecyl phthalate, didecyl phthalate, and the like. Examples of theadipic acid ester include dibutyl adipate, dihexyl adipate, dioctyladipate, di-2-ethylhexyl adipate, didecyl adipate, didodecyl adipate,and the like. Examples of the other plasticizer include a plasticizerhaving an ester portion such as dioctyl azelate, dibutyl sebacate,dioctyl sebacate, tricresyl phosphate, acetyl tributyl citrate, ortrioctyl trimellitate.

Forming grooves on the surface of the adhesive layer improves theadherence between the particles of the particle layer and the adhesivelayer. FIG. 4 is a sectional view of the adhesive layer in this case.FIG. 5 illustrates forms of the grooves.

FIG. 6 illustrates a process in a case where the adhesive layer is firstprovided on the transparent electrode side. Release films are attachedin advance on both surfaces of the adhesive layer having the grooves.One of the release films is removed to attach the surface without thegrooves on the transparent electrode. The film is flexible so that thefilm may be bent a little to attach the adhesive layer on thetransparent electrode without causing bubbles. Next, the transparentsubstrate having the particle layer formed thereon is brought intocontact with the adhesive layer (on the side having the grooves).Although the transparent substrate, the transparent electrode, and thelight-emitting layer cannot be bent, air is pushed out of the grooves bypressurizing the transparent substrate, and hence the particles of theparticle layer and the adhesive layer are brought into close contactwith each other. Note that, during the pressurization, an autoclave orthe like is used so that the pressure is applied to the entire element,to thereby suppress the damage to the element to such a low level as tobe negligible.

FIG. 7 illustrates a process in a case where the adhesive layer is firstprovided on the particle layer side. One of the release films is removedto attach the surface without the grooves on the transparent electrode.The film is flexible so that the film may be bent a little to attach theadhesive layer on the transparent substrate without causing bubbles.Next, the transparent electrode is brought into contact with theadhesive layer (on the side having the grooves). Air is pushed out ofthe grooves by pressurizing the transparent substrate, and hence thetransparent electrode and the adhesive layer are brought into closecontact with each other without causing bubbles. Note that, during thepressurization, an autoclave or the like is used so that the pressure isapplied to the entire element and hence the adherence between thetransparent electrode and the adhesive layer is improved, to therebysuppress the damage to the element to such a low level as to benegligible.

Referring to FIG. 8, a first embodiment is described.

In the light-emitting element according to the present invention, theparticle layer is provided on the transparent electrode via the adhesivelayer. The particles of the particle layer are formed on the transparentsubstrate. The light-emitting element is formed by the process of FIG. 6or 7. The formed element is contained in a casing. The light-emittinglayer may be reduced in light-emitting efficiency under the influence ofmoisture and oxygen. Therefore, sealing layers are provided at the endsthereof.

Referring to FIG. 9, a second embodiment is described.

As illustrated in FIG. 9, this embodiment has a feature that reflectivelayers are provided at ends of the transparent substrate. Lightextracted efficiently by the particle layer enters the transparentsubstrate, and then a part of the light exits from the ends of thetransparent substrate. The light irradiates the casing and isattenuated. The light is reflected by the reflective layers back intothe transparent substrate. Therefore, a part of the light is extractedby the particle layer to be reflected by the electrode under thelight-emitting layer, and is eventually emitted to the outside from thetransparent substrate, with the result that the improvement inlight-emitting efficiency may be attained.

Referring to FIG. 10, a third embodiment is described.

Of the light traveling toward the ends of the transparent substrate,only a part of the light exits from the ends, and the remaining part isreflected on the inner surfaces of the ends and does not exit from theends. Therefore, the particle layer and the adhesive layer are providedalso at the ends of the transparent substrate so that the light leaksfrom the ends of the transparent substrate. The light travels throughthe adhesive layer to strike the reflective layer, and as in the secondembodiment, is eventually emitted to the outside from the transparentsubstrate, with the result that the improvement in light-emittingefficiency may be attained.

Referring to FIG. 7, a fourth embodiment is described.

In FIG. 7, the transparent substrate in a state in which the adhesivelayer is attached after forming the particle layer is illustrated as the“transparent substrate with a film”. This substrate is movable as a partunless the release film is removed. The step of laminating thelight-emitting layer, the electrode, the transparent electrode, and thelike needs to be performed in a highly clean room. On the other hand, inthe case of forming the particle layer, where particles having theaverage particle size of 80 to 200 nm are handled, the cleanness isreduced by the scattering of the used particles when the transparentsubstrate having the particle layer formed thereon is produced in ahighly clean room, which possibly leads to negative effects such asreduced production yields of other parts and products. Therefore, whenthe “transparent substrate with a film” of FIG. 7, on which the processup to the adhesion of the adhesive layer is completed, is produced inadvance as a part in a separate room or by a different manufacturer, notonly a merit that a high light extraction efficiency may be attained forthe transparent substrate to be used in the light-emitting element, butalso a merit that the cleanness may be maintained in the step oflaminating the light-emitting layer, the electrode, the transparentelectrode, and the like is obtained.

Referring to FIGS. 11 and 12, a fifth embodiment is described.

When a “transparent substrate with a film” capable of covering aplurality of the light-emitting elements is used, a light-emittingelement having a plurality of light-emitting portions for onetransparent substrate may be formed. For a number of the light-emittingportions, operations of forming a particle layer on the transparentsubstrate and further forming an adhesive layer thereon may be performedat once. As described above, when the transparent layer, the particlelayer, or the adhesive layer is provided in common to the light-emittingportions, it is possible to reduce the time required for the production.

Referring to FIGS. 13 and 14, a sixth embodiment is described.

In attaching light-emitting elements to the casing of a light-emittingdevice, when adapters including electrode terminals are used, attachmentand detachment to and from the light-emitting device may be facilitated.Further, by providing adapters to two sides of the four sides, it ispossible to reduce the load on the adapters during the time when thelight-emitting elements are fixed to the casing of the light-emittingdevice. If the light emitting elements are fixed only at one side, whenthe light-emitting device is carried around, for example, a force isapplied only on the one side to which an adapter is provided so thatthere is a high chance of damaging the adapter. Therefore, a pluralityof adapters are provided in a plane in which the light-emitting elementsand the light-emitting device are brought into contact with each other.In FIG. 14, the adapters are provided to two sides so that the force isapplied across the plane of each light-emitting element and hence theforce applied per unit area becomes smaller, with the result that damageis less likely to occur even when the light-emitting device isrepeatedly carried around. Note that, in FIG. 13, the adapters areprovided to two adjacent sides, but may be alternatively provided toopposite sides.

Referring to FIGS. 14, 15, and 16, a seventh embodiment is described.

When a plurality of light-emitting elements may be attached as in thecasing of FIG. 14, it is possible to form a light-emitting device inwhich the plurality of light-emitting elements are attached asillustrated in FIG. 15. In FIG. 16, the light-emitting elements arearranged in two rows. By providing the plurality of light-emittingelements, even if the performance of one light-emitting element isreduced, a drop in the light-emitting amount is small as long as otherlight-emitting elements are normal. In addition, the light-emittingelement is easy to detach, and hence a normal light-emitting amount maybe immediately recovered by exchanging the light-emitting element withthe reduced performance with a normal one. Further, it is more preferredwhen wirings for the light-emitting elements are provided in parallel sothat, even if the light-emitting element with the reduced performance isremoved, the current to the other light-emitting elements is notblocked.

Referring to FIGS. 17 and 18, an eighth embodiment is described.

No problem occurs even if the light-emitting elements have a triangularshape. When adapters are provided to two sides of the light-emittingdevice as in the case of the light emitting elements having arectangular shape of FIG. 13, only one side is left with no adapter.Therefore, the bonding property to the casing is improved and the forceapplied to the adapters becomes smaller as compared to thelight-emitting elements having the rectangular shape, and as a result,impact resistance is improved over the light-emitting elements havingthe rectangular shape. Further, when the light-emitting elements havingtriangular and rectangular shapes are combined appropriately, it ispossible to form the light-emitting device having an octagonal shape asin FIG. 18. In this manner, an illumination device having a novel shape,which has hitherto been impossible to form, may be proposed to improvethe design.

1. A light-emitting element, comprising: a light-emitting layer providedbetween a transparent electrode and an electrode; a transparentsubstrate provided on a side of the transparent electrode that isopposite to a side on which the electrode is provided; a particle layerprovided between the transparent electrode and the transparentsubstrate; and an adhesive layer provided between the transparentelectrode and the particle layer, wherein the particle layer includesparticles having a refraction index that is higher than a refractionindex of the transparent electrode.
 2. The light-emitting elementaccording to claim 1, wherein the particles constituting the particlelayer have an average particle size of 80 to 200 nm.
 3. Thelight-emitting element according to claim 1, wherein the particlesconstituting the particle layer are formed of titanium oxide, zirconiumoxide, barium titanate, strontium titanate, or bismuth oxide.
 4. Thelight-emitting element according to claim 1, wherein the particle layerhas an average thickness that is less than an average particle size ofthe particles.
 5. The light-emitting element according to claim 1,wherein the adhesive layer is added with particles of an inorganicoxide.
 6. The light-emitting element according to claim 1, wherein theadhesive layer has a storage elastic modulus of 1 kPa or more and 100kPa or less.
 7. A light-emitting device comprising: the light-emittingelement according to claim 1; a casing; and a reflective layer providedbetween ends of the transparent substrate and the casing.
 8. Thelight-emitting device according to claim 7, wherein the particle layerand the adhesive layer are further provided between the reflective layerand the ends of the transparent substrate.
 9. A light-emitting devicecomprising: a plurality of the light-emitting elements according toclaim 1, wherein the transparent substrate, the particle layer, or theadhesive layer is provided in common to the plurality of thelight-emitting elements.
 10. A light-emitting device comprising: aplurality of the light-emitting elements according to claim 1; and aplurality of adapters provided in a plane in which the plurality of thelight-emitting elements and the light-emitting device are brought intocontact with each other.
 11. The light-emitting device according toclaim 10, further comprising wirings provided in parallel for theplurality of the light-emitting elements respectively for supplyingpower to the plurality of the light-emitting elements.
 12. Thelight-emitting device according to claim 7, wherein the light-emittingelement has a light-emitting surface of a triangular shape.
 13. Thelight-emitting device according to claim 7, wherein the light-emittingelement has a light-emitting surface of a triangular shape and arectangular shape in combination.
 14. A transparent substrate to beattached to a transparent electrode, comprising: a particle layerprovided between a transparent substrate and an adhesive layer; and arelease film provided on a side of the adhesive layer that is oppositeto a side on which the particle layer is provided, wherein the particlelayer includes particles having a refraction index that is higher than arefraction index of the transparent electrode, and wherein the adhesivelayer has grooves formed in a surface on a side on which the releasefilm is provided.
 15. A production method for a light-emitting element,the light-emitting element comprising: a light-emitting layer providedbetween a transparent electrode and an electrode; a transparentsubstrate provided on a side of the transparent electrode that isopposite to a side on which the electrode is provided; a particle layerprovided between the transparent electrode and the transparentsubstrate; and an adhesive layer provided between the transparentelectrode and the particle layer, the particle layer including particleshaving a refraction index that is higher than a refraction index of thetransparent electrode, the production method comprising the steps of:forming the particle layer on the transparent substrate; forming theadhesive layer on the transparent electrode; and attaching the particlelayer on the adhesive layer.